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GEM Detectors for LHCb and KLOE-2: Design, Construction, and Performance Analysis

This article provides an overview of the design, construction, and performance analysis of GEM detectors in the LHCb and KLOE-2 experiments, including their use in the Muon and Inner Tracker systems.

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GEM Detectors for LHCb and KLOE-2: Design, Construction, and Performance Analysis

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  1. GEM activity at the Laboratori Nazionali di Frascati M. Alfonsi LNF-INFN

  2. OUTLINE > 2000 • GEM in LHCb (coll. with CA-INFN) • GEM for Vertex/Inner Trackers • Other R&D: GEM luminometer > 2006 > 2007 M. Alfonsi, LNF

  3. GEM in LHCb collaboration LNF-INFN and CA-INFN(*) (*)CA-INFN: W. Bonivento, A. Cardini, D. Raspino, B. Saitta M. Alfonsi, LNF

  4. CP in B-meson system The LHCb GEM detector in M1R1 LHCb apparatus Muon detector: L0 high pT trigger + offline muon ID B0Sm+m- B0dJ/+K0S B0SJ/+ f All stations are equipped with small gap MWPCs with the exception of M1R1 station (area ~ 1 m2), that will be instrumented with triple-GEM detectors. About 20% of triggered muons will come from M1R1. The M1R1 station is placed in front of the calorimeters and very close to the beam pipe, so that low material budget,high rate capability and radiation tolerant detectors are required. M. Alfonsi, LNF

  5. The LHCb GEM detector in M1R1 M1R1 detector requirements: • Rate Capability up to ~ 500 kHz/cm2 • Station Efficiency > 96% in a 20 ns time window(*) • Cluster Size < 1.2 for a 10x25 mm2 pad size • Radiation Hardness 1.8 C/cm2 in 10 years (**) • Chamber active area 20x24 cm2 (*) A station is made of two detectors “in OR”. This improves time resolution and provides some redundancy (**) Estimated with 50 e-/particle at 184 kHz/cm2 with a gain of ~ 6000 M. Alfonsi, LNF

  6. 9.7ns 5.3ns 4.5ns 4.5 ns LHCb-GEM: R&D on fast gas mixtures The intrinsic time spread : s(t) = 1/nvdrift , where n is the number of primary clusters per unit length and vdrift is the electron drift velocity in the ionization gap. Garfield: Magboltz + Heed simul. To achieve a fast detector response, high yield and fast gas mixtures are then necessary • Ar/CO2/CF4 (45/15/40): • 10.5 cm/s @ 3.5 kV/cm • 5.5 clusters/mm fast & non flammable M. Alfonsi, LNF

  7. Aging measurements: summary • Local Aging: • performed with a high intensity 5.9 keV X-ray tube, irradiated area of about 1 mm2 (about 50 GEM holes). Integrated charge 4 C/cm2 25 LHCb years. • Large Area Aging: performed by means of the PSI M1 positive hadron beam, with an intensity up to 300 MHz and an irradiated area of about 15 cm2. Integrated charge 0.5 C/cm2 3 LHCb years. • Global Aging: performed at Casaccia with a 25 kCi 60Co source. Detectors were irradiated at 0.5  16 Gray/h. Integrated charge up to 2 C/cm2 12.5 LHCb years. Detailed information can be found at: P. de Simone et al., “Studies of etching effects on triple-GEM detectors operated with CF4-based gas mixtures”, IEEE Trans. Nucl. Sci. 52 (2005) 2872 M. Alfonsi, LNF

  8. LHCb-GEM: detector construction All the construction operations are performed in a class 1000 clean room. The detector is composed by three GEM foils glued on fiberglass (FR4) frames, then sandwiched between a cathode and anode PCBs, that are glued on a honeycomb structure panels. A M1R1 detector is realized coupling two of such chambers. A GEM foil stretching technique has been introduced: no spacer within the active area is required to maintain the gap  NO geometric dead area The mechanical tension (18kg/jaw  20 MPa), applied to the edge of the foil, is monitored with gauge meters. Kapton creep is negligible for this mechanical tension (see http: //www.dupont.com): inside elastic limit !!! The GEM foil stretching device M. Alfonsi, LNF

  9. G3 G2 G1 Cathode HV supply for GEM detectors A new floating channel HV device has been designed and realized specifically for LHCb GEM detectors, allowing a safer and more flexible detector operation(single channel voltage setting and current monitor) G. Corradi et al., “A novel High Voltage System for a triple GEM detector” NIM A 579 (2007) 96 M. Alfonsi, LNF

  10. 2.9ns r.m.s. LHCb-GEM: full size detector performances The performances of a full size detector, in almost final configuration, have been measured at the T11-PS CERN facility. Efficiency measured on the last test beam Ar/CO2/CF4=45/15/40 Drift = 3.5 kV/cm Transfer = 3.5 kV/cm Induction = 3.5 kV/cm Time resolution of two chambers in OR M. Alfonsi, LNF

  11. Cylindrical GEM R&D for KLOE-2 M. Alfonsi, LNF

  12. The Kloe Experiment at DAΦNE e+e- collider @ s = 1019.4 MeV Main KLOE upgrade for high-L (~1033 cm-2s-1) DANE: insertion of an Inner Tracker inside the Drift Chamber M. Alfonsi, LNF

  13. 25 cm 15 cm DC wall 60 cm KLOE-2 Inner Tracker Detector Requirements: • r×z≈ 200x500µmsingle layer spatial resolution for fine vertex reconstruction of Ks and η rare decays and interferometry measurements • 5 tracking layers with low material budget (< 1.5% X0): each is a triple-GEM detector • R  20sto preserve KLKsinterference • Rate capability 30  40 hits/plane/μs(< 50 kHz/cm2) M. Alfonsi, LNF

  14. Cylindrical GEM for KLOE-2 Inner Tracker THE IDEA: • We propose a low-mass, fully cylindrical and dead-zone-free GEM detector as Inner Tracker for the KLOE-2 experiment. • The IT is composed by five concentric layers of cylindrical triple-GEM detectors (C-GEM). • Each C-GEM is realized inserting one into the other the required five cylindrical structures made of very thin polyimide foils: the cathode, the three GEMs and the readout anode. • Very light detector: only 0.3% of X0 per layer inside the active area. HOW to do that? A cylindrical GEM electrode is obtained exploiting thevacuum bag technique, rolling the polyimide foil up on machined PTFEcylindrical mould. M. Alfonsi, LNF

  15. Stretching system with gauge meter to monitor mechanical tension Construction of a small size C-GEM We built a small size (  90mm, L  250 mm) C-GEM prototype using GEM foils from LHCb, while the anode and cathode electrodes were realized with 50 µm kapton foil with a mono-layer of 5 µm of Cu deposition (Sheldhal G2300). Standard drift/transfer1/transfer2/induction configuration has been used:3/2/2/2 mm M. Alfonsi, LNF

  16. Test of the small size C-GEM prototype The C-GEM prototype, operated withAr/CO2 = 70/30gas mixture, has been fully characterized with anX-ray gun (6 KeV) in current mode (no FEE). Excellent stability (no dark current, no sparks) is observed up to agas gain of 104, for a wide range of stretching tension (2 ÷12 kg/cylindrical electrode) (Ei= induction field) … and typical electron transparency curves of the standard planar triple GEM detector are reproduced M. Alfonsi, LNF

  17. Preliminary simulation of the junction line The construction procedure implies the presence of a singularity along thegluing junction linemade of bare Kapton (neither copper nor holes). The distorsion of the field lines still efficiently drives the electrons to the multiplication holes A slight drop to 98%efficiency is onlyobserved in the case of a track crossing perpendicularly the middle of the junction line. More detailed simulation studies and the measurements on the next prototypein constructionwill give us relevant hints on this issue. M. Alfonsi, LNF

  18. 1000 x 350 mm2 GEM active area patch of n.3 333x350 mm2 Construction of the full size proto • Diameter:  300 mm (KLOE-IT Layer 1) • Active length:  352 mm • Number of strips: 1538 (only 1D rφ view for simplicity) • Readout channels: 384 (money limitation) M. Alfonsi, LNF

  19. Cylindrical Electrodes status The GEM foils are ready: 333x350 mm2 active area, divided in 20 sectors The three foils composing the cathode has been glued together M. Alfonsi, LNF

  20. The vertical insertion system requires for very precise mechanics and linear bearing equipments. A precise 500 µm thick Teflon sheet is deposited on the Al-cylinder • Mechanics is ready • fiberglass cylindrical frames • cylindrical moulds • vertical insertion tool M. Alfonsi, LNF

  21. Preliminary tests of large foils extraction 200 mm diameter C-GEM Successfully tested at 500 V M. Alfonsi, LNF

  22. Prototype schedule • Readout anode foil delivery 11 september • Detector assembling 15 october • Preliminary cosmic ray test 25 october • Beam tests december • Final Inner Tracker Design July 2008 • Start construction Spring 2009 • Commissioning in KLOE-2 end of 2009 General schedule M. Alfonsi, LNF

  23. GEM luminometer for the DaΦne upgrade test M. Alfonsi, LNF

  24. e - GEM GEM chamber e + lead g FEE mother board with digital readout (64 channels) Small-size prototype On April 2007 a small GEM chamber has been installedon DaΦne for photon detectioncoming from theFinuda interaction region M. Alfonsi, LNF

  25. Photon beam spot 10 cm 2.4 cm 2.4 cm GEM chamber photons counting 64 pads 10 cm Official FINUDA luminometer Small-size prototype results Obtained with a 8x8 pad readout Pad dimension: 3x3 mm2 M. Alfonsi, LNF

  26. Final layout The luminometer will be installed next October in DaΦne IP1for the test of the machine upgrade GEM foils are ready and construction has already started GEM Luminometer M. Alfonsi, LNF

  27. Conclusions • GEMs in LHCb are going to be installed this winter • We are involved on the R&D of a very innovative Cylindrical GEM detector as low-mass inner tracker for the KLOE experiment • A beam luminometer for the test of DaΦne upgrade is under construction M. Alfonsi, LNF

  28. Spares M. Alfonsi, LNF

  29. Medical applications M. Alfonsi, LNF

  30. IMAGEM: GEM for imaging • Preliminary studies on a GEM detector for X-Ray and g detection: • X-ray (1-10 keV) are efficiently detected with usual Ar (e ≈10%) or Xe (e ≈ 100%) basedgas mixtures with gas conversion gaps of the order of 1 cm. • For detection of g in the energy range 140 - 511 keV metal (mainly Au) converter are needed (see previous section on HPPC). In both cases GEM seems to offer a practicable solution … M. Alfonsi, LNF

  31. IMAGEM: X-ray Using a 100x100 mm2 triple-GEM detector, a PCB with 1x1mm2 64 pads placed on a row, a FEE based on ASDQ chip (LHCb) and VME DAQ with scalers for count rates induced by 6 keV X-ray conversion in a defined time gate we perform preliminary imaging tests. M. Alfonsi, LNF

  32. IMAGEM: X-ray An X-ray movie has been realized with such triple-GEM detector operated with Ar+CO2=70+30 gas mixture. A rotating pencil box (with 2 pens inside) illuminated by a 6 keV X-Ray can be easily inspected. Each picture frame (30 pictures) has been kept in scanner mode (w/a Pb collimator) with a time gate of 100 ms. Each pixel of 1x1 mm2 is measuring 700 Hz. The X-ray gun behind the pencil box is operated with a filament current of only 30 mA. M. Alfonsi, LNF

  33. gamma IMAGEM: 140 keV g ray (preliminary) Different gamma converters have been considered for 140 keV gamma rays conversion. A GEM itself, or a Large Electron Multiplier (LEM) made with 0.5 mm thick FR4 layer drilled with 0.5 mm holes (1 mm pitch), with a gold deposition on the top side, and suitably polarized (no amplification, only collection and drifting photoelectrons is required), can be used as quite efficient converter for a triple-GEM detctor. The electrons produced are collected through the converter holes and drifted towards the usual triple-GEM device for amplification and detection. converter triple-GEM M. Alfonsi, LNF

  34. IMAGEM: 140 keV g ray (preliminary) This image has been obtained with a time gate of 4 sec, in scanner mode (w/Pb collimator). The maximum rate measured on a singlepad is 15 Hz with a background less than 2 Hz. • Four 99Tc (140 KeV) sources 10x2 mm2 wide have been put in front of the scanner system at a distance of 3 cm from the camera : • First two sources: 4 mm apart • Second two sources: 6 mm apart 10 mm 4 mm 6 mm M. Alfonsi, LNF

  35. LHCb – GEM Construction Spares M. Alfonsi, LNF

  36. Pad-PCB Cathode-PCB LHCb-GEM: detector construction Honeycomb PCB panels: The support panels of the GEM detector are realized coupling PCBs with FR4 copper cladback-planes with a 8mm thick honeycomb layer in between.Globally the panel has a material budget of the order few % of X0and a planarity ≤ 50mm (r.m.s.) Measurements of 12 PCB panels: the displacement from an average plane is of the order of 60 mm (rms) M. Alfonsi, LNF

  37. humidity probe HV supply R= 100 MH N2 Flow LHCb-GEM: detector construction All GEM foils are tested before frame gluing in order to check their quality. The test, sector by sector, is performed in a gas tight box. The gas box is flushed for about 1 hour with nitrogen in order to reduce the R.H. (<10%) before to start the test of the GEM foil The voltage to each GEM sector is applied through a 100 M limiting resistor in order to avoid GEM damages in case of discharges. A GEM is OK if, for each sector, I < 1 nA @ 500 V M. Alfonsi, LNF

  38. LHCb-GEM: detector construction  GEM framing Before gluing, the frame is cleaned and checked for broken fibers Araldite 2012 epoxy, 2 hours curing time, good handling properties & electricalbehavior,aging tested , is applied with a rolling wheel toolon the frame. The frame is then coupled with stretched GEM foil After epoxy polymerization the GEM foil is cut to size and 1 MW smd resistors are soldered on the HV bus of each of the six sectors. M. Alfonsi, LNF

  39. LHCb-GEM: detector construction  assembly (I) For chamber assembly we use araldite AY103 + HD991 with good electrical behavior & well-known aging properties(*) and 24 h curing time. (*)C. Altunbas et al., CERN-EP/2002-008; CERN PH-TA1-GS,(http://detector-gas-systems.web.cern.ch) The epoxy is applied with a rolling wheel tool on framed GEMs. The 3mm, 1mm, 2mm framed GEMs, plus an additional bare 1mm frame, for the induction gap, are positioned on the cathode PCB panel. The assembly operation is performed on a machined ALCOA reference plane, equipped with 4 reference pins. Over the whole structure a load of 80 kg is uniformly applied for 24h, as required for epoxy polymerization. M. Alfonsi, LNF

  40. LHCb-GEM: detector construction  assembly (II) Before the PCB pad panel gluing, HV connections of GEM foils are soldered on cathode PCB Inside the four reference holes, used for the chamber assembly, Stesalite bushings are inserted and glued with the Araldite 2012 epoxy. Bushings prevent gas leaks from the corners of the chamber and are used to hang-up the chamber on the muon wall The gas leakage of the produced chambers is less than 5mbar per day the humidity of the gas mixture is below 100ppmV with a flux of 80cc/min. The gain uniformity, measured with a high intensity 6keV X-ray beam, is ~10% M. Alfonsi, LNF

  41. LHCb-GEM: detector construction  assembly (III) Two triple-GEM detectors are coupled, through the four pin holes, with cathodes faced one to each other. FEE boards are installed along the detector perimeter and closed with a Faraday cage. The whole chamber, FEE and Faraday cage included, has a material budget of the order of 8% X0. M. Alfonsi, LNF

  42. LHCb-GEM: detector quality test N2 Ref chamber leak < 1 mbar/day equiv. ~ 50 ppm H2O @ 80 cc/min gas flow T, P Patm Chamber to test S1 S2 Gas leak test The gas leak rate measurement of a chamber is referred to a leak rate of a reference chamber (same volume, “no leak”), in order to take into account for atmospheric pressure and temperature variations. Both test and reference chambers are inflated in parallel, up toan overpressure of few mbar. The difference between P(S1) e P(S2) measures the gas leak rate of the test chamber M. Alfonsi, LNF

  43. LHCb-GEM: detector quality test X-ray tomography The gain uniformity, pad by pad, is measured with a high intensity 6.0 keV X-ray tube, measuring the current drawn by the detector. The drop on border pads is due to the large effective beam spot size . Gain uniformity  10% M. Alfonsi, LNF

  44. C-GEM Construction Spares M. Alfonsi, LNF

  45. 1 2 Construction steps: 1 - the GEM foil is rolled up on the cylindrical mould; 2 - the gluing of the GEM foil is performed with a bi-component epoxy along a 2÷3 mm overlap junction, where necessarily no GEM holes are present (representing a detector singularity) M. Alfonsi, LNF

  46. 3 3 - the cylinder is enveloped with a vacuum bag: vacuum is performed with a Venturi system; 4 - after curing cycle the GEM foil is easily removed from the cylindrical mould: the result is a perfect cylindrical GEM or cathode/anode electrode. 4 M. Alfonsi, LNF

  47. 5 6 5 – on each cylindrical GEM foil the 1 M HV limiting resistors are soldered on the corresponding six GEM HV sectors. 6 – before the final assembly, each cylindrical GEM foil is tested up to 500 V (the test has not been performed in a humidity controlled atmosphere). M. Alfonsi, LNF

  48. 8 7 7 – the cylindrical electrodes are inserted one into the other (cathode, GEM-1,2,3, anode) and then flanges are glued one to each other with araldite 2011. 8 – after the assembly, the C-GEM has been installed in a stretching system, equipped with a gauge meter allowing the monitoring and control of the mechanical tension applied to the prototype. M. Alfonsi, LNF

  49. Test of the small size C-GEM prototype The C-GEM prototype, operated with anAr/CO2 = 70/30 gas mixture, has been fully characterized with anX-ray gun ( 6 keV). During the test several gas parameters, such as T,P and RH, as well as the mechanical stretching tension applied to the prototype has been monitored. M. Alfonsi, LNF

  50. Designed at LNF, realized at CERN Strip (550 m) Pitch =650 m 100 m 650 µm strip pitch CSTRIPS ~ 50 pF GND 500 µm strip pitch Readout anode design M. Alfonsi, LNF

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